If I remmember correctly, mounting a 50mm prime with reverse ring to a Sigma 105mm lens on the cam body will give a magnification of 105/50=>2.1X.
For TS you may need to get a 55->58 step-up ring to be used together with a 58-52 reverse ring to mount the 2 lenses you mentioned. Tagotech sells these items.
Thanks everyone for your reply.....
Manage to get a 55 - 52 step down ring and then attached a 52-52 ring in front of it.
The 90 mm Tamron plus 50 mm was quiet fine. Although....one's gotta have a bright light source and a tony amount of shake ca throw the pic ofcourse. But it works.:thumbsup: